The present invention relates to a distance detection system for a vehicle, which images an object in a predetermined range and detects a distance in dependency on an imaged picture.
The vehicle such as an automobile is so convenient for transporting persons or articles that vehicles are used in our modern society. Accordingly, many systems for automatically avoiding accidents have been developed recently.
For automatically avoiding collision between the vehicles and the objects, it is very important to detect an obstruct on a running way of the vehicle. Such a system has already been developed as detecting the obstacle by using a radar (radiation detecting and ranging), an ultrasonic wave, or a laser (light amplification by stimulated emission of radiation).
However, it is a very complicated and difficult work to recognize a running route in real time, to detect the obstacle on the route, and to measure a distance and velocity to the obstacle. In particular, the above-mentioned system can detect only the object in a fixed direction by using the radar, the ultrasonic wave and the laser.
Furthermore, it is necessary to detect a place of the obstacle on the road. However, such an apparatus as mentioned above cannot have the sufficient information. Furthermore, it is necessary to detect the obstacle in a large area along the road having curves, and it is insufficient to detect the obstacle only in the fixed direction in the manner of the above-mentioned apparatus.
Accordingly, a distance measurement system is recently used as an effective method. The system images a sight as an object by a camera mounted on the vehicle to take pictures, and processes the pictures so as to obtain a distance between the vehicle and the object.
The distance measurement systems using the picture are divided into two techniques. One is to estimate the distance to the object by measuring a relative distance between a camera position and an image by a single camera. The other is to obtain the distance to the object by a principle of a triangulation after a plurality of pictures are imaged by a plurality of cameras or one camera which has several positions sequentially changed.
The technique for imaging a sight by the single camera is advantageous because little data are processed. And manufacturing cost is low because the object having various characteristics is extracted from two-dimensional images and the characteristics are shown in a manner that a white line indicates the plane.
For example, Japanese patent application laid-open No. 1-242916 (1989) discloses the technique which a television camera is mounted in a cabin near a center portion at a top of a front window, the obstacle and the white line on the road are detected in dependency on a luminance distribution pattern on a certain survey line in the image and the two-dimensional luminant distribution pattern, and the three-dimensional position of the white line and the obstacle is estimated in dependency on parameters of a directional and visual field.
However, an actual picture on the road have various objects such as buildings and trees in surroundings, so that it is difficult to precisely detect the various objects such as a running car in front, an oncoming car, a pedestrian, a pole for a telephone or electric light, a white line across a road, and the like, from such a two-dimensional picture. Furthermore, there is the problem that an estimation of the three-dimensional position has a large error when the three-dimensional position of a white line and the obstacle is estimated from a parameter of the television camera where the surface of the road is uneven and the vehicle is pitching.
Namely, a method of imaging by the single camera cannot always precisely extract the object from the two-dimensional picture because a plurality of various objects exist in the forward view while running. Furthermore, it makes the recognized result ambiguous because estimation of the position of the television camera is not always proper by such an inclined road as a slope.
On the other hand, the technique using triangulation and plurality of pictures can obtain a precise distance because a distance is obtained by a relative discrepancy of the position of the same object in left and right pictures.
For example, Japanese patent application laid-open No. 59-197816 (1984) discloses a method for calculating a three-dimensional position of an obstacle by using the principle of the triangulation in which two television camera are mounted on a front part of the vehicle, the obstacle is detected by a luminant distribution pattern of two dimension in dependency on respective images of each television camera, and so obtain the positional discrepancy on two pictures.
Furthermore, as disclosed in documents of the 22th Research and Lecture Meeting held by the Mechanical Engineering Institute on Oct. 20, 1989, two television cameras are attached to right and left front ends of the vehicle to image two pictures, each of the pictures is spatially differentiated to extract only a dark/light changing point, an image scanning of one of camera is delayed by a predetermined time to superpose on another picture, only a white line is extracted from the superposition of both pictures in dependency on the characteristics of the luminant distribution pattern included in the white line and width values of the pattern, and a distance between the vehicle and the extracted white line is calculated in dependency on the delayed time and the principle of the triangulation. The documents disclose the technology for calculating the three-dimensional position of the white line from short to long distance in the manner that such a processing is performed by continuously changing the delayed time.
Furthermore, as disclosed in Automobile Technology Magazine of Vol. 44, No. 4, 1990, pages 54-59, there is described a technology for calculating the three-dimensional position of the white line by the triangulation in the manner that two television cameras are mounted at right and left front ends of the vehicle, a white line is detected by the luminant distribution pattern in the two-dimensional window with respect to every picture of the television cameras, and the discrepancy of the white line on the two pictures of the right and left cameras.
The above prior art can prevent generation of large errors because two television cameras are used and the three-dimensional position is calculated by the triangulation. However, it is difficult for the above prior art to detect the white line and the obstacle as the object from the two-dimensional picture having various objects and background only by using the luminant distribution pattern. Therefore, even though the three-dimensional pictures have advantages in their use, the amount of the processing data is vast because matching between the right and left pictures must be repeated, thereby deteriorating processing speed.
In order to overcome the above deterioration, since a processing amount must be reduced and pre-processing must be performed, there must be generating binary data, detecting an edge, highly extracting the characteristic point and a set of the window with a decrease of information data. So that the distance must be measured only in the window or only for the object which can generate the binary data and the portion of the characteristic point such as edge or the like.
Accordingly, the prior art has the problem that the necessary object data are eliminated the data with respect to a pedestrian, an electric light or telephone pole, a white line and edges of the road because processing is done at high-speed. Therefore, resulting in the deterioration of the information data in the manner that only a specified portion is previously extracted from the picture and a distance of the only specified portion is obtained.